The present invention relates to a method for manufacturing biodegradable molded articles which are decomposable by bacteria, microbes, etc. in the soil.
Plastics are generally used as materials for molded articles such as containers, packaging materials, etc. However, the plastics have the following disadvantages which give rise to problems in their waste treatment after use. In such molded plastics, the biodegradability thereof is extremely low and sometimes a toxic gas is generated when they are incinerated. Thus, the disposal (burying, incinerating, compositing, etc.) of plastics has caused serious social and environmental problems.
Recently, in place of such plastics use has been made of biodegradable molded articles (hereinafter simply referred to as the molded articles) which can be decomposed by bacteria, microbes, etc. in the soil. The molded articles which are made from biodegradable materials. When such molded articles are buried in the soil, they are easily decomposed as mentioned above, thereby eliminating the problem associated with the waste disposal of the conventional molded articles made from plastics. Moreover, it is safe to use such molded articles, for example, as containers for foods.
Conventionally, the biodegradable molded articles are manufactured by placing biodegradable raw materials in a mold heated beforehand to a predetermined temperature, by application of conventional thermal conductive heating. In an alternative method, the biodegradable molded articles are formed in any desired shapes with an application of pressure by means of a high pressure press.
However, the above-noted conventional heating process has the following problems:
1) From the heated mold, heat is dissipated not only to the materials placed in the mold to be heated, but also into the atmosphere surrounding the mold, thereby resulting in poor energy efficiency.
2) Furthermore, because of this excess heat dissipation, the temperature of the atmosphere surrounding the manufacturing device increases, thereby resulting in an unfavorable working environment.
3) Since a long time is required for entirely transferring heat to the materials to be molded which are placed in the mold, it is difficult to complete the molding process in a short time, thereby resulting in low productivity.
4) In order to complete the process more quickly, the mold can be heated beforehand to a higher temperature. However, as a result, a great difference in temperature arises between the surface portion and the inside portion of the material to be molded, thereby presenting the resulting in a non-homogeneous structure of the molded articles.
5) Further, since the mold must be heated to a predetermined temperature beforehand, excess energy as well as time is required.
On the other hand, for example, the alternative method employing compression molding by means of a high-pressure press has the following problems:
1) The device itself is larger in size, and large-scale production facilities are required.
2) Loud noise and great vibrations occur in the manufacturing process, thereby resulting in an unfavorable working environment.
3) Since the method using a high-pressure press is dangerous, special care must be taken during its operation.